/*
 *    Thing Game Library
 *   Copyright (C)2005 - 2010 Eduardo Nunes Pereira (eduardonunesp at gmail dot com)
 *
 *   This program/library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 *   This program/library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 *    You should have received a copy of the GNU Lesser General Public
 * License along with this program/library ; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef __MATHUTILS_HPP__
#define __MATHUTILS_HPP__

/* A very fast function to calculate the approximate inverse square root of a
 * floating point value and a helper function that uses it for getting the
 * normal squareroot. For an explanation of the inverse squareroot function
 * read:
 * http://www.math.purdue.edu/~clomont/Math/Papers/2003/InvSqrt.pdf
 *
 * Unfortunately the original creator of this function seems to be unknown.
 */

inline float fastInvSqrt(float x)
{
    union { int i; float x; } tmp;
    float xhalf = 0.5f * x;
    tmp.x = x;
    tmp.i = 0x5f375a86 - (tmp.i >> 1); 
    x = tmp.x;
    x = x * (1.5f - xhalf * x * x); 
    return x;
}

inline float fastSqrt(float x)
{
    return 1.0f / fastInvSqrt(x);
}

inline float weightedAverage(float n1, float n2, float w)
{
    if (w < 0.0f)
        return n1; 

    if (w > 1.0f)
        return n2; 

    return w * n2 + (1.0f - w) * n1; 
}

#endif
